Spatial 3-D displays such as Actuality Systems Inc.'s Perspecta® Display create 3-D imagery that fills a volume of space and that appears to be 3-D to the naked eye. One such spatial 3-D display is described in U.S. Pat. No. 6,554,430, “Volumetric three-dimensional display system.” This display is formed in the shape of a transparent dome and contains a rotating screen orientated vertically within the dome. As the screen spins it displays a previously recorded image for example at every 1 degree of rotation for 360 degrees. Human persistence of vision combines these images to create a 3-D view of the previously recorded image. This display with its vertical dome shape can be placed on top of a tabletop for example. One feature of this type of 3-D display is that the imagery provides motion parallax in every direction; in other words, it is a full parallax display.
Some 3-D displays provide motion parallax information with only one degree of freedom. A well-known family of 3-D displays with restricted motion parallax are horizontal parallax only (HPO) displays. Known HPO displays provide motion parallax along one axis, normally in the horizontal direction, corresponding to left-right motion; when the user moves vertically, the 3-D image appears to track the user's motion because of the lack of vertical parallax information. Displays of this type are taught in: U.S. Pat. No. 3,178,720, “Three dimensional unaided viewing method and apparatus,”; D. J. DeBitetto, “Holographic Panoramic Stereograms Synthesized from White Light Recordings,” in Applied Optics, Vol 8(8), pp. 1740-1741 (August 1969); and U.S. Pat. No. 5,132,839, “Three dimensional display device.”
Another type of restricted parallax display can be called the theta parallax only (TPO) display, which provides motion parallax for a user moving angularly around the display. A 360-degree hologram is a display hologram of this type, as described in R. Hioki and T. Suzuki, “Reconstruction of Wavefronts in All Directions,” in Japanese Journal of Applied Physics, Vol. 4, p. 816 (1965); and in T. H. Jeong, P. Rudolf, and A. Luckett, “360° Holography,” in Journal of the Optical Society of America, Vol. 56(9), pp. 1263-1264 (September 1966). A cylindrical hologram is another display of this type. As taught in the present application, one embodiment described below is a new example of a TPO display and is a circular display located in a top or in the middle of a table for use with multiple users sitting around a conference room table.